An Improved Method for Fabrication of Ag-GO Nanocomposite with Controlled Anti-Cancer and Anti-bacterial Behavior; A Comparative Study

Abstract

In this study, two green procedures for Silver-Graphene Oxide (Ag-GO) nanocomposite synthesis were investigated. As a common method, AgNO₃ was first loaded on the GO surface and then was reduced and stabilized by walnut green husk extract, producing Ag-GO-І. As an innovative approach, GO was first exposed to the extract and then the AgNO₃ was added as the second step, producing Ag-GO-П. Physicochemical properties, antibacterial and cytotoxicity activity of both nanocomposites were subsequently studied comparing with free silver nanoparticles (AgNPs) and pure GO. Based on the results, exposure of GO to the extract, as a reducing agent, at the first/last step of the synthesis process resulted in the fundamental differences in the final products. So that, high amounts of agglomerated silver nanoparticles were formed between the GO sheets, when using the common method, whereas in Ag-GO-П, small AgNPs were formed on the GO sheets without aggregation, entirely covering the sheets. Antibacterial and cytotoxic behavior of these nanomaterials could be compared as AgNPs > Ag-GO-П > Ag-GO-І. It is assumed that these differences are due to control of unwanted nucleation in the synthesis process that Ag nanoparticles are smaller with less agglomeration when the GO surfaces are pre-treated with reducing agent.

Figure 1

UV-Visible spectra of the colloidal Ag-GO nanocomposites (a) Ag-GO-І and (b) Ag-GO-П indicating the increase, and subsequently decrease in the peak intensity along with a redshift with the passing of time.

Figure 2

XRD spectrum of (a) pure GO, (b) Ag-GO-І and (c) Ag-GO-П. Peaks assigned with an asterisk (*) represent the Silver, and the black square (■) corresponds to the Graphene Oxide.

Figure 3

FT-IR spectra of the pure GO and GO exposed to Walnut green husk extract. The lower FT-IR peak intensity of the extract modified GO than pure GO confirms the reduction of functional groups in this compound.

Figure 4

Representative field emission scanning electron microscopy (FESEM) images of pure GO (a), Ag-GO-I (b,d) and Ag-GO-II (c,e) as well as their particles size distribution, (f,g), respectively.

Figure 5

EDS spectrum of (a) Ag-GO-І and (b) Ag-GO-II, showing differences of the amount of silver and carbon elements in two synthesized nanocomposites, and EDS-map of (c) Ag-GO-І and (d) Ag-GO-II.

Figure 6

Antibacterial activity of pure GO, M-GO, Ag-GO-І, Ag-GO-П and free AgNPs against (a) E. coli, (b) P. aeruginosa, (c) S. aureus.

Figure 7

Viability of MCF-7 cells after 72 hours exposure to 20–100 µg.ml⁻¹ of (a) GO or MGO, (b) walnut green husk extract, (c) Ag-GO-І, (d) Ag-GO-П and (e) AgNPs. (f) shows a summary comparison of cytotoxic activity of the nanomaterials after 48 hours exposure to 60 µg.ml⁻¹. Triplicate incubations for each treatment were conducted in each independent experiment. P values were calculated using one-way ANOVA test (*P < 0.05).